Investigating Transient Overvoltages in 150(170) kV Gas-Insulated Substations

I am a PhD researcher in the High Voltage Technologies group at TU Delft, working in collaboration with TenneT TSO to assess transient overvoltage stresses in SF₆ and SF₆-free GIS for the Dutch transmission grid.

I am currently seeking technical collaboration with GIS switchgear manufacturers who may be willing to share non-confidential or confidential-under-agreement GIS drawings, layout data, component parameters, and insulation design information for research purposes.

Who I am

My name is Benard Makaa, and I am a PhD researcher in the High Voltage Technologies group at TU Delft. My research focuses on transient overvoltages in gas-insulated substations within the Dutch transmission system, with particular attention to insulation coordination, SF₆-free GIS technology, and the possible application of 145 kV-rated switchgear in 150(170) kV grid environments.

This work is being carried out in collaboration with TenneT TSO, the transmission system operator for the Netherlands. The research supports the broader technical question of how high-voltage substations can transition toward lower-emission insulation technologies while maintaining reliability, safety, and compliance with insulation-coordination requirements.

The transition away from SF₆ is one of the most important technical challenges facing high-voltage switchgear today. For transmission system operators, the challenge is not only to replace an insulating gas, but to preserve reliability, insulation coordination, operational flexibility, and long-term asset performance. For manufacturers, the challenge is to demonstrate that new SF₆-free GIS technologies can meet real grid stresses, not only standard laboratory test conditions.

The work focuses on TRV, SOV, and VFTO stresses, with the aim of evaluating whether selected 145 kV SF₆-free GIS technologies can be safely and selectively applied in 170 kV grid environments.

Why this research matters

The high-voltage industry is entering a critical transition period. SF₆ has enabled compact and reliable GIS for decades, but its very high global warming potential has made SF₆ reduction and replacement a strategic priority for utilities, manufacturers, regulators, and researchers.

At the same time, practical grid requirements do not always align neatly with available SF₆-free equipment ratings. In the Dutch transmission grid, the 150 kV system is treated according to the 170 kV IEC equipment class, and TenneT documentation explicitly notes that the 150 kV system is based on 170 kV-rated switchgear and may operate close to that voltage level. It also cautions that 145 kV components cannot simply be upgraded to 150 kV without careful technical assessment.

This creates an important research question for future substation design: can selected 145 kV SF₆-free GIS technologies be applied safely in specific 150(170) kV environments, provided that actual transient overvoltage stresses, insulation margins, and mitigation requirements are properly quantified?

Main research question

The central research question is whether 145 kV SF₆-free GIS can be safely and selectively applied in 150(170) kV transmission-grid environments without compromising insulation coordination, operational reliability, or long-term asset performance.

This question cannot be answered from rated voltage alone. It requires a realistic assessment of the electrical stresses that GIS insulation experiences during actual grid events. My research therefore quantifies transient overvoltages using time-domain electromagnetic transient simulations, supported where possible by manufacturer data, grid data, and experimental validation.

The study focuses on three critical classes of transient stress:

The aim is to identify where 145 kV SF₆-free GIS may be technically feasible, where 170 kV equipment remains necessary, and where mitigation measures such as surge arresters, RC damping, controlled switching, layout optimisation, or shielding may create sufficient insulation margin.

The outcome will be a data-driven insulation-coordination framework that can support TenneT’s technical decision-making, assist manufacturers in understanding grid-specific stress requirements, and contribute to a credible transition toward SF₆-free high-voltage substations.

Why manufacturer data is essential

Accurate GIS transient studies depend strongly on the physical and electrical representation of the switchgear. Generic models are useful for early screening, but they cannot fully capture manufacturer-specific differences in GIS layout, conductor geometry, enclosure configuration, disconnector arrangement, capacitances, travelling-wave paths, and internal insulation distances.

For this reason, I am seeking collaboration with GIS manufacturers who can support the research by sharing representative technical data. The data does not need to reveal commercially sensitive design details unless both parties agree on confidentiality conditions. Even anonymised, simplified, or representative data can significantly improve the realism of the simulations.

Data I am currently looking for

I am currently looking for technical information related to both SF₆ GIS and SF₆-free GIS, especially at 145 kV and 170 kV rated voltage levels.

Relevant data includes:

What manufacturers gain by collaborating

A manufacturer who contributes data to this research can benefit in several ways:

Contact Details:

Please reach out to me through these email addresses: b.m.makaa@tudelft.nl or benard.makaa@tennet.eu

My research supervisors include:

Prof.ir.Dr Marjan Popov
Prof.ir.Peter Vaessen
Dr.ir.Dennis van der Born

From Tennet TSO:

André Lathouwers
Kostas Velitsikakis
Krithika Gunasekaran
Theodosis Beskas